Herb Gross defines inverse functions using the same ideas as in Lesson 17 on functions: Start with input x, apply function f, find the output y. Then use y as the input into a new program, the inverse program, which determines a new output which is the SAME as the original input, x. In other words, the inverse function undoes what the original function has done to the x. Herb supplies many familiar examples, including graphs, so that the new language becomes clear. This material and much more is also available online at www.adjectivenounmath.com.